Examination of visual field (namely, a perimetry) is performed to diagnose a constriction of visual field which is a symptom of glaucoma and so on. In the conventional perimetry, the visual field of the subject is measured by showing an eye-target at a specific point in front of an eye of a subject and having the subject answer a question whether he or she can see the eye-target. Such an examination is a subjective examination based on a subjective answer of the subject, and a visual field range of the subject is identified by measuring the visual field multiple times while changing the showing position of the eye-target one after another. In such a subjective examination, there was a problem that an inspection result is easily swayed by a physical condition and concentration and so on of the subject and an accurate examination can not be done. Furthermore, because a series of operations of showing the eye-target and then having the subject answer have to be repeated many times, there are also problems that it takes a long time to do the inspection and a burden on the subject is large.
Folia opthalmologica Japonica (p. 733-737, Volume 49, Number 9, 1998) discloses a perimeter capable of performing an objective perimetry which does not depend on the subjective answer of the subject. In this perimeter, in order to measure the visual field of the subject, a fixed eye-target is projected on a screen provided in front of the eyes of the subject, and a light stimulus eye-target is projected at a plurality of positions on the screen one after another in a condition where the subject is gazing at the fixed eye-target so as to give a light stimulus to a retina of the subject, and a miotic response of the pupil by the light stimulation (namely, a pupillary light reflex) is detected.
Furthermore, Japanese Non-examined Patent Publication No. 5-146404 and Japanese Non-examined Patent Publication No. 2004-216118 disclose a perimeter which objectively measures the visual field of the subject by showing a fixed eye-target and a light stimulus eye-target using a light emitting device such as a light-emitting diode and detecting the presence or absence of the pupillary light reflex at the time when the light stimulation is given to the subject.
In such an objective perimeter, the darker the background luminance to the light stimulus eye-target is, the easier the detection of the pupillary light reflex becomes. But, when the background luminance is too dark, the light of the light stimulus eye-target is scattered, and therefore the light stimulus is not given to an accurate position of the retina of the subject. Furthermore, it takes a long time for the pupil of the subject to adapt to the darkness of the background, whereby the inspection time becomes long. On the other hand, when the background luminance is too bright, the brightness difference between the background and the light stimulus eye-target becomes small, and the pupillary light reflex also becomes small, and therefore, the detection of the reaction becomes difficult. Furthermore, it is preferable that the size of the light stimulus eye-target and stimulus intensity thereof are changed according to the subject.
As mentioned above, in the objective perimeter, it is preferable that the background luminance, the brightness of the eye-target, and the size of the eye-target and so on are adjustable freely. But, in the above mentioned conventional perimeter, because the eye-target is projected on a screen or the light stimulus eye-target is shown by using a light-emitting diode, there was a problem that it is not possible to easily adjust the background luminance, the brightness of the eye-target, and the size of the eye-target.